Lube basestocks are commonly used for the production of lubricants, such as lubricating oils for automobiles, industrial lubricants and lubricating greases. They are also used as process oils, white oils, metal working oils and heat transfer fluids. Finished lubricants consist of two general components, lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
According to the American Petroleum Institute (API) classifications, lube basestocks are categorized in five groups based on their saturated hydrocarbon content, sulfur level, and viscosity index (Table 1). Lube base oils are typically produced in large scale from non-renewable petroleum sources. Group I, II, and III basestocks are all derived from crude oil via extensive processing, such as solvent extraction, solvent or catalytic dewaxing, and hydroisomerization. Group III base oils can also be produced from synthetic hydrocarbon liquids obtained from natural gas, coal or other fossil resources. Group IV basestocks, the poly (alpha olefins) (PAO), are produced by oligomerization of alpha olefins, such as 1-decene. Group V base oils include everything that does not belong to Groups I-IV, such as naphthenics, polyalkylene glycols (PAG) and esters.
TABLE 1API ClassificationGroup IGroup IIGroup IIIGroup IVGroup V% Saturates<90≧90≧90PolyAll others% S>0.03≦0.03≦0.03alpha-not belong-Viscosity80-12080-120≧120olefinsing toIndex (VI)(PAO)Group I-IV
Natural oils derived from biological sources are sometimes used as lubricants, but to a small scale, due to their poor low-temperature properties and hydrolysis instability. The triglyceride esters in natural oils are often hydrolyzed to yield fatty acids, which can be subsequently converted into esters as synthetic lubricants.
For environmental, economical, and regulatory reasons, it is of interest to produce fuels, chemicals, and lube oils from renewable sources of biological origin. So far only esters of renewable and biological origin have been used in applications such as refrigeration compressor lubricants, bio-hydraulic oils and metal working oils. In automotive and industrial lubricants, esters from biological sources are used in very small fractions as additives due to technical problems as well as their high prices. For example, ester base oils can hydrolyze readily producing acids, which in turn cause corrosion on lubricating systems.
In contrast, lube basestocks consisting of hydrocarbons from biological sources do not have those technical problems associated with esters from same sources. Most common biological sources for hydrocarbons are natural oils, which can be derived from plant sources such as canola oil, castor oil, sunflower seed oil, rapeseed oil, peanut oil, soy bean oil, and tall oil, or derived from animal fats. The basic structural unit of natural oils and fats is a triglyceride, which is an ester of glycerol with three fatty acid molecules having the structure below:
wherein R1, R2, and R3 represent C4-C30 hydrocarbon chains. Fatty acids are carboxylic acids containing long linear hydrocarbon chains. Lengths of the hydrocarbon chains most commonly are 18 carbons (C18). C18 fatty acids are typically bonded to the middle hydroxyl group of glycerol. Typical carbon numbers of the fatty acids linked to the two other hydroxyl groups are even numbers, being between C14 and C22.
For the purpose of this disclosure, when all the fatty acid chains in a triglyceride have more than 14 carbon atoms, the triglyceride is considered a long-chain fatty acid triglyceride. When one or more of the fatty acid chains in a triglyceride has less than 14 carbon atoms, the triglycerides are considered medium-chain triglycerides.
In the field of fuels, so-called renewable source components are now required both in the US and Europe. Although there is no imminent requirement for lube products currently, generating premium basestocks from renewable sources on a large scale is attractive for the same policy reasons that led to the imposition of regulations in the higher volume fuel area. In fact, with recent advances in biofuels, natural oils are becoming increasingly available as feedstocks that provide fuel value comparable to that of petroleum oils. Converting these bio-feeds to lubes can give significant value uplift.
WO 2007/068800 describes a process for producing a saturated hydrocarbon component from a biological starting material comprising an oligomerization step, an optional prehydrogenation step, a deoxygenation step and an optional hydroisomerization step.
US 2009/0014354 mentions a process for producing base oils from a biological starting material comprising a condensation step selected from ketonization, aldol condensation, alcohol condensation and radical reaction and a combined hydrodefunctionalization and isomerization step under pressure from 0.1 to 15 MPa at the temperature from 100 to 500° C. in the presence of a bifunctional catalyst.
Recent researches focus on chemical transformations in a series of catalytic steps requiring separate reactors for each individual step as well as optimization of conditions in each reactor. Many process steps involve clean-up of a reaction mixture or isolation of a desired product from a mixture. For example, fatty acids and alcohols are produced by hydrolysis of fatty acid triglycerides. Hydrolysis is typically conducted by treating the triglyceride with an acid solution, and is sometimes followed by extraction with an organic solvent, and finally recovery of the organic solvent. The acid is consumed in the process and therefore, hydrolysis can add significant cost to the lube processes disclosed in the art.
US 2010/0018108 describes a method for producing base oil and diesel or other transportation fuel comprising processing a triglyceride-containing vegetable oil to effect oligomerization and deoxygenation of unsaturated fatty acid components contained therein to provide for an oligomerized mixture, isomerizing the oligomerized mixture over an isomerization catalyst to yield an isomerized mixture, and distilling the isomerized mixture to produce a base oil and a diesel fuel.